Well, first of all, a star is a large ball of gas that undergoes nuclear fusion. So by this definition, a comet is not a star, since it is made of ice and dirt that is running around in space. Stars shine on their own or omit light within their own wavelengths, but comets only shine because they reflect light, hence they are not a star. Comets are created by gravitational pulls and formations broken off of actual planets when they are destroyed, which is why it takes a long time. So as for the tail of the comet, it is more unique. Radiation from the sun pushes dust particles faraway from the coma, forming a dust tail, while charged particles from the sun convert a number of the comet's gases into ions, forming an ion tail. Since comet tails are shaped by sunlight and also solar radiation, they always point far from the sun.
Well, as we all know that a star is not considered as a star because a comet usually revolutes the sun in elliptical orbit whereas a star doesn't revolutes a sun.
Eruption with low silica tends to be nonexplosive. The type of lava is Basaltic, flows easily because of low viscosity (low gas content- originates in the mantle). This type of lava comes from shield volcanoes (low angle slopes and gentle)- eg. Manua Loa Volcano and Hawaii.
